1. Field of the Invention
This invention relates to the field of current detectors for use in electromagnetic actuator drive circuits. More specifically, this invention relates to those current detectors for detecting a solenoid current in those electromagnetic actuator drive circuits which control the opening of an electromagnetic valve based on such a solenoid current.
2. Description of Related Art
There are several known methods for controlling electromagnetic actuator drive circuits which control the opening of an electromagnetic valve based on a solenoid current, and these methods may be broadly divided into two classes. A first class is those methods which control the solenoid by supplying a solenoid transistor driver circuit with a DC voltage. A second class is those methods which control the solenoid by supplying a solenoid transistor driver circuit with a pulse voltage signal.
It is also known to detect the current in the solenoid by means of a solenoid current detection resistor, connected in series with the solenoid and the solenoid transistor driver circuit, which detects the solenoid current based on the voltage appearing across the resistor. The detected solenoid current may then be used for executing feedback control, as is well known in the art, so as to adjust the solenoid current value to correspond with an external adjusting control.
In the first class of methods noted above for controlling electromagnetic actuator drive circuits, one problem which has arisen in the art is that the solenoid transistor driver circuit is constantly driven in its active region, as shown for example in U.S. Pat. No. 4,378,766, published Apr. 5, 1983, hereby incorporated by reference. This causes larger than desired power consumption and larger than desired production of waste heat. Consequently, the second class of methods noted above has become preferred in the art. One such method is shown in Japanese Laid-open Patent Publication No. 57-137901, published Aug. 25, 1982, and in U.S. Pat. No. 4,458,487, published July 10, 1987, both hereby incorporated by reference.
In the second class of methods noted above for controlling electromagnetic actuator drive circuits, one problem which has arisen in the art is that the voltage detected across the solenoid current detection resistor will vary with the pulse voltage signal. To determine an accurate solenoid current value, the this varying voltage must be smoothed with a filter. This causes a time delay between the input of a correcting control signal to the solenoid actuator, and the solenoid current which is measured in response.